Comfortable and ergonomic office equipment, readily adaptable to a user's individual needs is a prerequisite for creating an office work environment conducive to maximum productivity. Chairs are an integral part of any office environment and features which can be adjusted to meet a user's posture requirements play a pivotal role in contributing to a user's comfort level. In particular, chairs having height adjustable backrests or seat backs are important for adapting the chair to the user's posture needs. The chair seat back is attached to the rest of the chair by a support arm attached at one end to the seat back and the other end of the support arm is engaged by a seat back height adjustment mechanism attached to the chair.
Known seat back height adjustment mechanisms include a cam rotatably mounted in a bracket. The cam comprises a shaped cylindrical rod having a handle attached thereto such that rotation of the rod via the handle provides a cam action. The cam is rotatably mounted between the side walls of the mounting bracket spaced from a back wall of the bracket. The support arm is slidably received between the bracket back wall and the cam. To adjust the seat back to the desired height, the cam is first rotated so that it disengages from the support arm thereby leaving the support arm free to be adjusted; once the support arm is adjusted to the desired height the cam is rotated to engage the support arm thereby compressing the arm between the cam-shaped portion and the back wall of the bracket to lock the seat back at the desired vertical height.
One drawback to this arrangement is that the user requires the use of two hands to take the necessary steps to adjust the seat back to the desired height: one hand to vertically move the seat back and hold it at the desired height, and the other to rotate the cam using the handle. Furthermore, in order for the cam to engage and lock the seat back support arm, a positive locking action between the cam and support arm is required, the user must rotate the cam such that the cam is tightly engaged, compressing the arm between it and the back wall of the bracket.
Accordingly, it would be advantageous to provide a chair seat height adjustment mechanism which can be manipulated using one hand and having a passive locking means.